-LRB- CNN -RRB- -- Frankel and Black Caviar . The burning question in the horse racing world is whether its two biggest stars will ever get together .

While that once meant `` Who would win if they went head to head ? '' now all the talk is about what they might produce given time and a bit of privacy .

And , just as importantly , how much would that coupling be worth in the mega-bucks breeding stakes ?

Both horses have swept all before them in illustrious careers . Frankel has posted nearly $ 3 million in prize money for the Juddmonte Farm stables , with an unbeaten run in 12 encounters . Black Caviar has also done well for her owners , with 22 wins on courses in Australia and the UK in the past four years .

Frankel is now rated as the best performer on the flat in the world by race statistics company Timeform -- which since 1948 has been using a mathematical equation comparing race results to the weight of the horse plus distance run to create a hierarchy which is used in many form guides for racegoers and owners .

While performance on the turf is not always a leading indication of performance in retirement , top bloodstock experts say Frankel 's lifetime value in stud could be around $ 155 million .

`` Frankel will have the pick of the best mares when it is time for him to stud , and there is no mare out there at the moment attracting as much attention as Black Caviar , '' says Johnny McKeever , who has 25 years of experience in buying horses which have gone on to win major Group One meets around the world .

`` If you own a good mare and you can afford the stud fees Frankel will command , why would n't you want to put forward your horse to breed with him ? '' he told CNN .

And that initial stud fee is set to break the current world record held by Irish horse Sea The Stars , who earned nearly $ 7 million in prize money from a series of wins in major Group One races such as the Prix de L'Arc de Triomphe and the Epsom Derby .

`` Sea The Stars commanded a $ 133,000 fee at the start , so it is not impossible that Frankel 's first valuation will be around $ 155,000 and that may be a touch on the conservative side , '' McKeever said .

`` There are no guarantees with this , and the performance of a horse on the course is not always a marker it can be successful in creating the next generation . But Frankel 's achievements in racing , coupled with his bloodline , means he would be more likely to sire a good racing performer . ''

Bloodstock valuations have come down from the crazy prices of a decade ago , when horses would sell for $ 10 million as purchasers found it difficult to secure a return on their investment with falling prize money at racecourses around the world . But the high end of the market is still very lucrative , with yearlings from top breeds selling at $ 2 million .

The statistics show exactly why a Frankel-Black Caviar horse would be much fancied on a racetrack .

Frankel commands a Timeform rating of 147 , which is well above the average for a Group One race winner of 129 . Black Caviar is the highest rated filly of all time , rated at 136 .

`` Ever since he was a three-year-old , Frankel has seemed determined to get better and better , '' Timeform 's flat racing editor David Johnson told CNN .

`` He had already rated at 140 by his first 2000 Guineas victory last year , and by the Queen Anne Stakes at Ascot this year he had overtaken Seabird as the greatest horse since records began .

`` It seems a shame that his owners do not want to test him at the longer distances , and I think what we are possibly seeing now is a winding down of his attendances with the chance he will be at stud by next year . It is unlikely we will see him at the Breeders ' Cup or the Prix de L'Arc de Triomphe . ''

Black Caviar , who turns six this month , may be retiring at roughly the same time . Trainer Peter Moody is still undecided whether she will get a few more run-outs as part of a farewell tour of Australian courses , or whether June 's Ascot appearance was her last race .

The cult status achieved by both horses has spawned a lucrative sideline business , with everything from Black Caviar cufflinks priced at $ 42 to a $ 15 Frankel coffee mug available through online stores . Goodwood 's recent sellout crowd was largely down to the attendance of Frankel and both have their own Twitter pages .

Despite the desires of the racing industry to see these giants of flat racing procreate , there are two hurdles to overcome .

First is whether Frankel 's owners want this to happen . There is a feeling in the industry at the moment that , come the day Juddmonte decide to put him out to stud , they may want him to pair with mares already in their stable so they get to reap the rewards of whatever he will produce .

However , that may be just for the first crop of the next generation , and they may be happy to let Frankel go to stud elsewhere later on in his career .

The second problem might be a little bit harder to overcome . The path of true love is not easy for humans , and it is no less an issue for horses .

`` At the end of the day there is no guarantee that Frankel and Black Caviar will take to each other . They might not like one another , much like some humans are unlikely to mate , '' McKeever said .

`` That is why , however much racehorse fans would like to see this happen , and however much money is offered to make it happen , the only two beings that can ensure it does are Black Caviar and Frankel . ''

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Frankel has won $ 1.8 million in prize money so far but he could be worth $ 155 million in stud

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Top yearlings used to fetch $ 10 million at auction but the market has deflated in recent years

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Black Caviar is the highest-rated filly of all time according to racehorse performance experts

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Both horses are mini marketing enterprises with a range of branded clothing and gifts